The invention relates to a motor-driven machine tool with a drive motor, the motor shaft of which is driven in rotation, with a tool drive shaft, which is driven in rotation or in oscillation about its longitudinal axis, and with a coupling drive for converting the rotational movement of the motor shaft into a driving movement of the tool drive shaft.
Machine tools of this type have been known for decades and are used in many different ways particularly as hand-held electric tools. In this context, there are both machines in which the tool drive shaft executes a rotating rotational movement, such as, for example, in drilling machines or angle grinders. Furthermore, in recent years, machines with an oscillating driving movement of the tool drive shaft have become increasingly common, and in this case the tool drive shaft can be driven in oscillation about its longitudinal axis. Oscillating machines tools of this type are used in many different ways for grinding, cutting or sawing, etc.
Particularly in the case of machine tools driven in oscillation, but also in specific machine tools having a tool drive shaft driven in rotation, such as in angle grinders, there is a problem that vibrations may occur which have an adverse effect upon the service life of the machine and are felt by the user to be a disadvantage.
If the motor shafts and the tool drive shaft are not oriented concentrically or axially parallel to one another, one-sided stresses upon the bearings occur, and, in course of time, overloads, premature defects or failures may possibly arise.
In machine tools driven in oscillation, the rotary driving movement of the motor shaft is converted into an oscillating driving movement of the tool drive shaft by means of a suitable coupling drive. In this case, a relative movement may occur between the drive motor and the coupling drive as a result of vibrational decoupling or damping. In this case, too, concentric and axially parallel orientation of the motor axis and tool drive shaft is therefore no longer possible.
EP 2 139 647 B1 discloses a machine tool driven in oscillation, according to the precharacterizing clause of Claim 1, in which length compensation, for example using a star-shaped profile which engages into a bore with corresponding profiling, is provided between the drive shaft and motor drive shaft.
However, a design of this kind allows only length compensation in the region of the drive chain.